Normally, I open a Cygwin terminal window by clicking on a Windows icon
which is an alias to a .BAT file which prepares environment variables
for my Cygwin session and then invokes mintty thusly:
start /b C:\cygwin64\bin\mintty -i/Cygwin-Terminal.ico -s80,57 -

Nothing unusual there, but I have come to rely on the chere package,
which seems to invoke mintty directly, so doesn't prepare my
environment variables.